1. The Field of the Invention
The present invention relates generally to multiplexed high speed communications systems, methods, and devices. More particularly, embodiments of the invention relate to systems and methods for transparently providing scalable and movable DWDM usage onto CWDM networks.
2. The Relevant Technology
Computer and data communications networks continue to develop and expand due to declining costs, improved performance of computer and networking equipment, the remarkable growth of the internet, and the resulting increased demand for communication bandwidth. Such increased demand is occurring both within and between metropolitan areas as well as within communications networks, such as wide area networks (“WANs”), metropolitan area networks (“WANs”), and local area networks (“LANs”). These networks allow increased productivity and utilization of and data, and the processing of voice, data, and related information at the most efficient locations.
Moreover, as organizations have recognized the economic benefits of using communications networks, network applications such as electronic mail, voice and data transfer, host access, and shared and distributed databases are increasingly used as a means to increase user productivity. This increased demand, together with the growing number of distributed computing resources, has resulted in a rapid expansion of the number of fiber optic systems required.
Through fiber optics, digital data in the form of light signals is formed by light emitting diodes or lasers and then propagated through a fiber optic cable. Such light signals allow for high data transmission rates and high bandwidth capabilities. Other advantages of using light signals for data transmission include their resistance to electro-magnetic radiation that interferes with electrical signals; fiber optic cables' ability to prevent light signals from escaping, as can occur electrical signals in wire-based systems; and light signals' ability to be transmitted over great distances without the signal loss typically associated with electrical signals on copper wire.
Another advantage in using light as a transmission medium is that multiple wavelength components of light can be transmitted through a single communication path such as an optical fiber. This process is commonly referred to as wavelength division multiplexing (WDM), where the bandwidth of the communication medium is increased by the number of independent wavelength channels used. To accomplish wavelength division multiplexing, several specialized optical components are used, including demultiplexers (demuxes), multiplexers (muxes), mux/demux modules, and optical add drop multiplexers (OADMs).
A demultiplexer generally takes as its input an optical transmission that includes a number of individual signals, with each signal being transmitted using a particular wavelength of light. An exemplary optical demultiplexer is shown in FIG. 1 and designated generally as 100. The optical demultiplexer 100 has an input port 102. The input port 102 receives a multiplexed transmission 104. In the present example, the multiplexed transmission 104 has four individual signals, each of different wavelengths, which are designated in this example as λ1, λ2, λ3, and λ4, as indicated in FIG. 1A. In this example, the optical demultiplexer 100 is a passive device, meaning that no external power or control is needed to operate the device. Although the optical demultiplexer 100 is a passive device, it should be noted that active devices can be used in optical demultiplexing as well. Using a combination of passive components, such as thin-film three-port devices, mirrors, birefringent crystals, etc., the optical demultiplexer 100 separates the multiplexed signal 104 into its constituent parts. Each of the individual wavelengths, each representing a separate signal on a communication channel, is then output to one of output ports 106, 108, 110, 112.
A multiplexer functions in the inverse manner as the demultiplexer. Multiplexers can often be constructed from demultiplexers simply by using the output ports 106, 108, 110, 112 as input ports and the input port 102 as an output port.
An optical device that combines the functionality of a demultiplexer and a multiplexer is known as a mux/demux. An exemplary mux/demux is shown in FIG. 2 and designated generally as 200. The mux/demux 200 has a multiplexed input port 202 that accepts as its input a multiplexed transmission 104. The multiplexed transmission 104 is separated into its constituent parts and output to demultiplexed output ports 204, 206, 208, 210. In a multiplexing operation, demultiplexed input ports 212, 214, 216, 218 accept as their input individual signals, with each signal being encoded on a different optical wavelength. The individual signals are combined into a multiplexed transmission and output to the multiplexed output 220 from output port 105.
An OADM is a component designed to extract an individual signal from the multiplexed transmission while allowing the remaining signals on the multiplexed transmission to pass through. The OADM also has an add port that can be used to remix the extracted signal with the multiplexed transmission or to transmit other data onto the fiber-optic network. An example of an OADM is shown in FIG. 3 and designated generally as 300. The OADM 300 is designed for bi-directional data communication. In optical networks, to distinguish the direction of data travel, the directions are referred to as east and west directions. In FIG. 3, data that travels in an easterly direction travels to the right of the OADM 300. Data the travels in a westerly direction travels to the left of the OADM 300.
Now illustrating the functionality of the OADM 300, a multiplexed transmission 104 is input into the east input port 302. The OADM 300 is designed for a specific wavelength or, more precisely, a band of wavelengths. For example, if the particular multiplexed transmission has four wavelengths, including a 1510 nanometer wavelength, a 1530 nanometer wavelength, a 1550 nanometer wavelength, and a 1570 nanometer wavelength, and the OADM 300 is designed to extract signals transmitted on the 1550 nanometer wavelength, the OADM may in fact extract any signal within a 12 nanometer bandwidth centered about the 1550 nanometer wavelength. As such, any wavelength between 1544 and 1556 nm is extracted by the OADM 300. In the present example, an individual signal 304 is extracted from the multiplexed transmission 104 and output to a device existing on the network, such as a network node 306, through the east drop port 308.
All other wavelengths remaining on a the multiplexed transmission continue through the OADM 300 and exit through an east output port 310, where they may continue to propagate on the fiber-optic network. If the OADM is a bi-directional module, such as OADM 300, a multiplexed transmission traveling in a westerly direction enters the OADM 300 at the west input port 318, drops the particular signal through the west drop port 320, adds a signal through the west add port 322, and propagates the remaining wavelengths through the west output port 324.
The network node 306 has two transceiver modules 312. In one embodiment, the transceiver modules may be GigaBit Interface Converters (GBICs). The transceiver modules 312 have input ports for accepting optical signals so that the signals can be converted to a data signal useful by the network node 306 and output ports for generating optical signals from the network node 306 so that data from the network node 306 may be propagated on the fiber-optic network. Optical signals from the network node 306 may be propagated onto the fiber-optic network such that they travel in an easterly direction by inputting the signals into the east add port 326 or propagated to the fiber-optic network, such that they travel in an westerly direction by inputting the signal signals into the west add port 322. By using an OADM that is bi-directional, redundancy may be added to the optical fiber network to provide for such contingencies as broken fibers in one of the directions. Optical add drop modules, such as OADM 300, are generally passive devices and are constructed using thin-film three-port devices, fused fiber devices, or other passive components.
A relatively high density of wavelengths can be transmitted using dense wavelength division multiplexing (WDM) and coarse wavelength-division multiplexing (CWDM) applications where the individual wavelength communication channels are closely spaced to achieve higher channel density and total channel number in a single communication line.
CWDM allows a modest number of channels, typically eight or less, to be stacked in the 1550 nm region of the fiber called the C-Band. CWDM transmission may occur at one of eight wavelengths: typically 1470 nm, 1490 nm, 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm, 1610 nm. The channel spacing between each of the adjacent channels is 20 nanometers and the bandwidth of each of the channels is 12 nanometers. The 12 nanometer bandwidth means that the wavelength of a particular channel may vary up to six nanometers to either side of the nominal wavelength. Such an arrangement helps to prevent cross-talk between adjacent channels, such as that which occurs when the signals drift into an overlapping area.
Coarse wavelength division multiplexing systems, as the name implies, have relatively wide channel spacings. As such, more cost-efficient components that exhibit more wavelength drift may be used in the implementation of the network. Factors that can cause wavelength drift in the fiber optic network include temperature variations of the lasers transmitting the optical signals, temperature variations of the individual components that make up the network, and physical bending stresses on fibers within the optical network.
A second type of wavelength division multiplexing that may be used in a metro area network is DWDM (dense wavelength division multiplexing). As its name suggests, DWDM networks have much narrower channel spacings than CWDM networks, for example 0.8 nanometers or 0.8 nanometers. As such, more channels and hence more bandwidth can be provided on the network. The tradeoff for this higher network capacity is that more expensive components exhibiting less temperature stress and physical stress sensitivities must be used. Dense wavelength division multiplexing technology was originally intended for long-haul networks requiring hundreds of wavelengths built with expensive high-performance optics. Although DWDM systems provide superior scalability compared to CWDM systems, they do so at an increased cost per wavelength.
Although it is readily apparent that DWDM systems provide greater capacity than CWDM systems, CWDM systems are already installed throughout the world in a variety of networks. It would be relatively expensive to replace CWDM systems with DWDM systems, including transceivers, multiplexers, demultiplexers, and other devices in order to upgrade and obtain the greater capacity. This is particularly true considering the rapid development of data transfer technologies. It is therefore financially impractical to frequently update or replace legacy CWDM systems to support the most recent DWDM technologies.
Accordingly, there is a continuing need to increase data transfer capacity in communication systems. It would represent a significant advance in the art to be able to provide that increased capacity over existing systems.